Non-invasive neural interface

ABSTRACT

A neuromodulator includes an electromagnetic (EM) wave generator configured to generate EM waves remote from a patient and to direct the EM waves to one or more target regions within the patient. Frequencies of the EM waves fall outside a range of frequencies that activates neurons. Intersection of the EM waves in each target region creates envelope-modulated electric and magnetic fields having one or more frequencies that fall within the range of frequencies that activates neurons. The neuromodulator includes control circuitry configured to control parameters of the EM waves produced by the EM wave generator. The neuromodulator may use feedback based on one or more of patient input and/or sensing of physiological signals in order to close the loop and control the EM waves.

BACKGROUND

Neuromodulation involves stimulating nerves to alter nerve activity andis one of the most exciting emerging therapies for treatment of a broadrange of diseases and conditions. For example, neuromodulation has thepotential to provide important and life changing therapy for intractablepain, spinal cord injuries, headaches, Parkinson's disease, Alzheimer'sdisease, depression, and many other afflictions.

SUMMARY

Some embodiments are directed to a system that includes aneuromodulator. The neuromodulator includes an electromagnetic (EM) wavegenerator configured to generate EM waves remote from a patient and todirect the EM waves to one or more target regions within the patient.Frequencies of the EM waves fall outside a range of frequencies thatactivates neurons. Intersection of the EM waves in each target regioncreates envelope-modulated electric and magnetic fields having one ormore frequencies that fall within the range of frequencies thatactivates neurons. The neuromodulator includes control circuitryconfigured to control parameters of the EM waves produced by the EM wavegenerator.

According to some aspects, the system further includes a receiverconfigured to receive EM waves from the target region wherein thereceived EM waves are modulated by neural activity signals within thetarget region.

Some embodiments involve a process that includes generatingelectromagnetic (EM) waves at a location remote from a patient, whereinfrequencies of the EM waves fall outside a range of frequencies thatactivate neurons. The EM waves are directed to one or more target regionwithin the patient where they intersect. In each target region,intersection of the EM waves creates envelope-modulated electrical andmagnetic fields having frequencies falling within the range offrequencies that activate neurons. The characteristics of theenvelope-modulated electrical and magnetic fields can be altered bychanging the parameters of the intersecting EM waves. The process mayfurther include receiving EM waves modulated by a neural activity signalgenerated by neural activity within the target region.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram illustrating a neuromodulation process inaccordance with some embodiments;

FIG. 2 is a block diagram of a neuromodulator in accordance with someembodiments;

FIG. 3A provides a graph of a first EM wave having the form sin (x);

FIG. 3B provides a graph of a second EM wave having the form sin(x+0.1x), superimposed on the first EM wave of FIG. 3A;

FIG. 3C depicts the combination of the first and second EM waves ofFIGS. 3A and 3B, the combination forming envelope-modulated fieldshaving the form sin (x)+sin (x+0.1x) in accordance with someembodiments;

FIG. 4 depicts another example of a neuromodulator comprising multipletarget regions in accordance with some embodiments;

FIG. 5 is a flow diagram illustrating a process of providingneuromodulation with feedback in accordance with some embodiments;

FIG. 6 is a block diagram of a neuromodulator that includes one or moredevices for obtaining patient information in accordance with someembodiments;

FIG. 7 is a flow diagram of a process that includes detecting neuralactivity in one or more target regions in accordance with someembodiments; and

FIG. 8 is a block diagram of a system that is capable or stimulatingneural activity and sensing neural activity in one or more targetregions within a patient in accordance with some embodiments.

The figures are not necessarily to scale. Like numbers used in thefigures refer to like components. However, it will be understood thatthe use of a number to refer to a component in a given figure is notintended to limit the component in another figure labeled with the samenumber.

DETAILED DESCRIPTION

With an increasing trend of various forms of mental affliction amonghumans in present society, being able to sense and address parts of thebrain on demand—either to sense or stimulate or stimulate andsimultaneously sense neural activity has important therapeuticconsequences. Approaches discussed herein involve temporal interferencephased-array stimulation and/or sensing (TIPS) that takes advantage oftemporal interference between two electromagnetic (EM) waves to providelocalized steerable neural interaction. Apart from a huge potential intreating and understanding mental illnesses, the approaches discussedherein provide an invaluable tool for researchers in neuroscience.

The neuromodulation devices disclosed herein can provideminimally-invasive and/or feedback-controlled neuromodulation and/orneural sensing within the brain and/or for peripheral nerves such as thevagus nerve or various other neural tissue in the body. The ability toselectively sense and/or stimulate nerve fascicles within a relativelysmall region enables treatment of a wide-range of peripheral and centralnervous system disorders with targeted therapies.

Turning now to FIG. 1 there is shown a flow diagram that illustrates aneuromodulation process in accordance with some embodiments.Electromagnetic (EM) waves are generated 110 at one or more locationsremote from the patient. For example, the remote locations may be spacedapart from the patient by a few centimeters, a meter, or more than ameter such that the source of the EM waves does not come into contactthe patient. The EM waves have frequencies that exceed the range offrequencies capable of causing activation of neurons, e.g., frequenciesgreater than about 100 kHz. The EM waves are directed 120 to one or moretarget regions within the body of the patient where the EM wavesintersect 130 with one another. In each target region, the intersectingEM waves create 140 envelope-modulated electric and magnetic fields thatinteract 150 with the neural tissue and neurons within the targetregion. In some implementations, therapeutic neurostimulation can beprovided by electric and/or magnetic fields that provide stimulationabove the threshold required for activation of neurons. In someimplementations, therapeutic neurostimulation can be by electric and/ormagnetic fields that are below the threshold required for activation ofthe neurons. In some embodiments, the magnitude and/or degree ofmodulation of the envelope-modulated fields stimulate the neurons in thetarget region causing them to fire. In other embodiments, the magnitudeand/or degree of modulation of the envelope-modulated fields are belowthe threshold required for activation of the neurons in the targetregion.

FIG. 2 is a block diagram of a neuromodulator 200 in accordance withsome embodiments. The neuromodulator 200 includes an EM wave generator210 that generates and transmits multiple EM waves. For example, asshown in FIG. 2, the EM wave generator 210 may generate first and secondsignals that are transmitted by components 211, 212 as first and secondEM waves 281, 282. The EM waves 281, 282 are directed to one or moretarget regions 260 within the body 290 of a patient. In FIG. 2, thetarget region 260 is shown within the patient's brain, however, it willbe appreciated that target regions may be located within other parts ofthe patient's body.

The EM waves 281, 282 intersect within the target region 260. Linearsuperposition of the EM waves 281, 282 in the target region 260 causes atemporal variation in the electric and magnetic fields 270 in the targetregion 260 that differs from the temporal variation of the incident EMwaves 281, 282. The linear superposition of the waves 281, 282 createsenvelope-modulated electric and magnetic fields 270 in the target region260. Modulation of the envelope occurs at a frequency which is adifference between the frequencies of the incident EM waves. The firstEM wave 281 may be expressed mathematically as A₁ sin w₁(x), where A₁represents the amplitude of the first EM wave 281 and w₁ represents thefrequency of the EM wave 281. The second EM wave 282 may be expressedmathematically as A₂ sin(1+α)w₁(x), where A₂ represents the amplitude ofthe second EM wave 282 and (1+α)w₁ represents the frequency of thesecond EM wave 282. In the target region 260, the first and second EMwaves combine to form envelope-modulated fields which can be expressedas A₁ sin w₁(x)+A₂ sin(1+α)w₁(x). Note that a could be negative.

For example, FIG. 3A provides a graph of a first EM wave 381, sin (x),and FIG. 3B provides a graph of a second EM wave 382, sin (x+0.1x),superimposed on the first EM wave 381. As depicted in FIG. 3C, the firstand second EM waves 381, 382 combine to form envelope-modulated fields383, sin (x)+sin (x+0.1x) in this example.

Returning to FIG. 2, the neuromodulator 200 includes a controller 250that can control parameters of the EM waves 281, 282, such as frequency,phase, and/or amplitude. Changing the parameters of the EM waves 281,282 can be used to modify one or more characteristics of theenvelope-modulated fields 270 in the target regions 260. For example,the controller 250 may change one or more of frequency, amplitude, andmodulation depth of the envelope-modulated fields 270 by modifying thefrequency, phase, and/or amplitude of the EM waves 281, 282.

Each target region 260 may have volume of less than about 5 cm×5 cm×5cm, or less than 125 cm³) or even less than about 30 cm³, or 2 cm×2 cm×2cm, or less than about 8 cm³. In some embodiments, the controller 250may control the parameters of the first and second EM waves 281, 282such that a maximum amplitude of the envelope-modulated fields 270 fallwithin the target region 260. In some embodiments, the controller 250may control the parameters of the first and second EM waves 281, 282such that a maximum degree of modulation of the envelope-modulatedfields 270 fall within the target region 260.

In some embodiments the EM waves 281, 282 that intersect within thetarget regions 260 are composites of multiple EM waves generated by theEM wave generator 210 of the neuromodulator 200. The neuromodulator 200may comprise phased array that produces multiple EM waves that undergoconstructive and/or destructive interference as they travel toward thepatient. The controller 250 controls the parameters of the multiple EMwaves, e.g., frequency, phase, and/or amplitude, generated by the phasedarray to beam steer and/or focus the intersecting EM waves to at leastone target region 260.

In some implementations, the frequencies of the first and second EMwaves 281, 282 may operate within FDA-approved WiFi bands, such as the2.45 GHz frequency. These FDA-approved bands have been the subject ofextensive research showing that these frequencies do not cause adversereactions in people. In some embodiments, the frequencies of the EMwaves 281, 282 may be greater than about 1 MHz and the frequencies ofthe envelope-modulated electric and magnetic fields are less than about100 kHz. In some embodiments, the frequencies of the EM waves may begreater than about 150 kHz and frequencies of the envelope-modulatedelectric and magnetic fields are less than about 100 kHz.

FIG. 4 depicts another example of a neuromodulator 400 in accordancewith some embodiments. Neuromodulator 400 includes an EM generator 410capable of generating EM waves 481, 482, 483, 484 that intersect atmultiple target regions 461, 462 within the patient's body 490. Asdepicted in FIG. 4, the target regions 461, 462 may be in the patient'sbrain or at other locations. EM waves 481, 482 intersect in targetregion 461.

The first EM wave 481 may be expressed mathematically as A₁ sin w₁(x),where A₁ represents the amplitude of the first EM wave 481 and w₁represents the frequency of the EM wave 481. The second EM wave 482 maybe expressed mathematically as A₂ sin(1+α)w₁(x), where A₂ represents theamplitude of the second EM wave 482 and (1+α)w₁ represents the frequencyof the second EM wave 482. In the target region 461, the first andsecond EM waves 481, 482 combine to form envelope-modulated fields 471which can be expressed as A₁ sin w₁(x)+A₂ sin(1+α)w₁(x).

The third EM wave 483 may be expressed mathematically as B₁ sin w₂(x),where B₁ represents the amplitude of the second EM wave 483 and w₂represents the frequency of the EM wave 483. The fourth EM wave 484 maybe expressed mathematically as B₂ sin(1+β)w₂(x), where B₂ represents theamplitude of the second EM wave 484 and (1+β)w₂ represents the frequencyof the fourth EM wave 484. In the target region 462, the third andfourth EM waves 483, 484 combine to form envelope-modulated fields 472which can be expressed as B₁ sin w₂(x)+B₂ sin(1+β)w₂(x).

As previously discussed, the controller 450 may control one or moreparameters of one or more of the first, second, third, and fourth EMwaves 481-484 to control characteristics of the envelope-modulatedfields 471, 472 respectively created in the target regions 461, 462.Additionally or alternatively, using a phased array and the technique ofconstructive and destructive interference, the controller 450 maycontrol one of more parameters of multiple EM waves generated by theneuromodulator to beam steer and/or focus the composite EM waves 481-484to the target regions 461, 462

In some embodiments, the parameters of the intersecting EM waves can bealtered by the controller based on patient information provided to thecontroller. FIG. 5 is a flow diagram illustrating a process of providingneuromodulation with feedback. According to these processes EM waves aregenerated 510 at one or more locations remote from the patient whereinthe source of the EM waves does not come into contact the patient. TheEM waves have frequencies that exceed the range of frequencies capableof causing activation of neurons. The EM waves are directed 520 to oneor more target regions within the body of the patient where the EM wavesintersect 530 with one another. In each target region, the intersectingEM waves create 540 envelope-modulated electric and magnetic fields thatinteract 550 with the neural tissue within the target region. Thecontroller may include communications circuitry that allows thecontroller to receive 560 patient information from a device configuredto gather information about the patient. The patient information may beobtained by sensors attached to the patient or implanted within thepatient, for example. The patient information may alternatively oradditionally be gathered by a device that provides a user interfaceallowing the patient or another operator to enter information. Thecontroller controls parameters 570 of the intersecting EM waves to altercharacteristics of the envelope-modulated fields within the targetregions based on the patient information. The patient information mayalso be obtained by analyzing the signal reflected back, in order todetermine the overlaying modification that has been caused to theoriginal impinging radiation.

FIG. 6 is a block diagram of a neuromodulator 600 in accordance withsome embodiments. The neuromodulator 601 includes an EM wave generator610 that generates and transmits multiple EM waves. For example, asshown in FIG. 6, the EM wave generator 610 may generate first and secondsignals that are transmitted by components 611, 612 as first and secondEM waves 681, 682. The EM waves 681, 682 are directed to one or moretarget regions 660 within the body 690 of a patient. In FIG. 6, thetarget region 660 is shown within the patient's brain, however, it willbe appreciated that target regions may be located within other parts ofthe patient's body.

The EM waves 681, 682 intersect within the target region 660. Linearsuperposition of the EM waves 681, 682 in the target region 660 causes atemporal variation in the electric and magnetic fields in the targetregion 660 that differs from the temporal variation of the incident EMwaves 681, 682. The linear superposition of the waves 681, 682 createsenvelope-modulated electric and magnetic fields 670 in the target region660. Modulation of the envelope occurs at a frequency which is adifference between the frequencies of the incident EM waves 681, 682.

The neuromodulator 600 includes a controller 650 that can controlparameters of the EM waves 681, 682, such as frequency, phase, and/oramplitude. Changing the parameters of the EM waves 681, 682 can be usedto modify one or more characteristics of the envelope-modulated fields670 in the target regions 660.

The controller 650 may be programmed to control the characteristics ofthe envelope-modulated fields 670 to provide a prescribed therapy or toachieve (or approach) a specific patent condition. For example, thecontroller 650 may change one or more of frequency, amplitude, andmodulation depth of the envelope-modulated fields 670 by modifying thefrequency, phase, and/or amplitude of the EM waves 681, 682.

According to some embodiments, the patient information device 641comprises one or more sensors. FIG. 6 shows two possible locations forthe patient information device 641—one proximate to the site of thestimulation and one farther from the stimulation site. In general, theremay be one or multiple patient information devices located within, on,or around the patient. The patient information devices may communicatedirectly with the controller 650 or may communicate with another device,such as a hand-held device. The patient information device 641 providessensed patient information to the controller 650 which modifies the EMwaves 681, 682 based on the sensed patient information. For example, oneor more sensors may be attached to the patient 690, implanted within thepatient 690, or otherwise disposed to sense patient information. Thepatient information device 641 may be coupled to the controller 650through a wired or wireless communications link, for example. Accordingto some implementations, the patient information device 641 may beincorporated within an implantable diagnostic or therapeutic device,such as a cardiac pacemaker, that wirelessly communicates with theneuromodulation controller 650. In some embodiments, the patientinformation device 641 measures biological signals such as heart rate(HR), blood pressure (BP), respiratory rate (RR), body temperature,etc., non-invasively.

According to some embodiments, patient information may be obtained froma device 642 that provides a user interface which allows the patient oranother operator to enter the patient information and/or record thepatient response to a series of questions. The patient informationentered may include measured values, e.g., heart rate, respiration rate,temperature, and/or may include subjective information, such as mood,perceived pain level, and/or other perceptions of psychological state,tracking and responding to certain visual or auditory stimuli in thefield of view of the user.

One or both patient information devices 641, 642 may be configured tomonitor dynamically changing physiological patient information, e.g.,heart rate, respiration rate, blood pressure, body temperature, etc.,and to communicate the patent information to the controller 650. Inresponse, the controller 650 alters one or more parameters of the EMwaves 681, 682 that create the envelope-modulated fields 670 within thetarget region 660. Components of the neuromodulator 600, e.g., thecontroller 650 and/or the patient information devices 641, 642 maysynthesize and analyze both stimulation and sensing data by utilizingself-learning algorithms, and may be configured to adapt the EM waves641, 642 in real-time to enhance therapeutic efficacy.

Based on the patient information obtained from devices 641, 642, thecontroller may develop a dynamic profile of biological conditions thatoccur in response to stimulation of the nerves within the target region660. Optimal profiles of biological conditions that provide accuratefeedback control for the neuromodulation function may be developed foreach target region 660.

The approaches described with reference to FIGS. 1-6 illustrate a“write-in” capability of the neuromodulator that can be used to provideneural stimulation to the patient. For example, the neuromodulator canbe configured to create envelope-modulated electric and magnetic fieldsin target regions of a patient's body that provide a prescribedneuromodulation therapy to the target regions. In some embodiments, theenvelope-modulated fields may have a field strength sufficient toactivate neurons in the target regions causing them to fire. In someembodiments, the field strength of the envelope modulated fields may bebelow the threshold to activate the neurons, providing a sub-thresholdtherapy which sensitizes the neurons for activation but does not causeactivation. In some implementations, the approach described above may beused with an existing technology such as superconducting quantuminterference devices (SQUID) magnetoencephalography (MEG), in whichdifferent target regions of the brain are activated using theneuromodulator described above while the SQUID MEG maps out magneticfields from the brain.

In addition to the “write-in” capability of the neuromodulator, a systemmay have “read-out” capability that allows monitoring of the neuralactivity within the target region. The neural activity within a targetregion can be read out when the neural activity within the target regionmodulates the envelope-modulated fields (also referred to as theinterference signal) created by superposition of the EM waves in thetarget region. The modulation of the interference signal by neuralactivity results in EM waves that deviate from EM waves that areexpected in the absence of neural activity. The EM waves are received ata receiver and the modulation caused by neural activity extracted fromthe received EM waves.

FIG. 7 is a flow diagram of a process that includes detecting neuralactivity in one or more target regions in accordance with someembodiments. Electromagnetic waves are generated 710 at one or morelocations remote from the patient wherein the source of the EM wavesdoes not come into contact the patient. The EM waves have frequenciesthat exceed the range of frequencies capable of causing activation ofneurons. The EM waves are directed 720 to one or more target regionswithin the body of the patient where the EM waves intersect 730 with oneanother. In each target region, the intersecting EM waves create 740 aninterference signal comprising envelope-modulated electric and magneticfields. Optionally in some embodiments, the interference signal isconfigured to stimulate 750 the neurons within the target region.

The interference signal is modulated by a neural activity signalgenerated by neural activity within the target region. The modulatedinterference signal is transmitted from the target region as aneural-activity-modulated EM wave. The neural-activity-modulated EM waveis received 760 by a receiver. Optionally the neural activity signal canbe extracted 770 from the neural-activity-modulated EM wave and analyzed780 to obtain information about the neural activity. Optionally, theneural activity signal can be used to control 790 neural stimulation atthe target region and/or can be used to control other therapies and/orprocesses.

FIG. 8 is a block diagram of a system 800 that is capable or stimulatingneural activity and sensing neural activity in one or more targetregions 860 within a patient 890 in accordance with some embodiments.The system 800 includes an EM wave generator 810 that generates andtransmits multiple EM waves. For example, as shown in FIG. 8, the EMwave generator 810 may generate first and second signals that aretransmitted by components 811, 812 as first and second EM waves 881,882. The EM waves 881, 882 are directed to one or more target regions860 within the body 890 of a patient. In FIG. 8, the target region 860is shown within the patient's brain, however, it will be appreciatedthat target regions may be located within other parts of the patient'sbody.

The EM waves 881, 882 intersect within the target region 860. Linearsuperposition of the EM waves 881, 882 in the target region 860 causes atemporal variation in the electric and magnetic fields 870 in the targetregion 260 that differs from the temporal variation of the incident EMwaves 881, 882. The linear superposition of the waves 881, 882 createsenvelope-modulated electric and magnetic fields, also referred to as theinterference signal in the target region 860. Modulation of theinterference signal occurs at a frequency which is a difference betweenthe frequencies of the incident EM waves 881, 882.

The interference signal may be further modulated by a neural activitysignal generated by neural activity in the target region. The neuralactivity may be stimulated by the interference signal, for example. Themodulated interference signal is transmitted from the target region 860as a neural-activity-modulated EM wave 824. The system 800 includes areceiver 823 configured to receive the neural-activity-modulated EM wave824.

The system 800 includes a controller 850 coupled to the EM wavegenerator 811 and the receiver 823. The controller 850 can be configuredto demodulate the received neural-activity-modulated EM wave 824 toextract the neural activity signal from the neural-activity-modulated EMwave 824. The controller 850 can be configured to control parameters ofthe EM waves 881, 882, such as frequency, phase, and/or amplitude.Changing the parameters of the EM waves 281, 882 can be used to modifyone or more characteristics of the interference signal in the targetregions 860. For example, the controller 850 may change one or more offrequency, amplitude, and modulation depth of the interference signal bymodifying the frequency, phase, and/or amplitude of the EM waves 881,882. In some implementations, the controller 850 may change theparameters of the EM waves 881, 882 based on the neural activity signalextracted from the neural-activity-modulated EM wave 824. For example,the controller 850 may change the characteristics of the interferencesignal, e.g., the amplitude and/or degree of modulation until the neuralactivity signal extracted from the neural-activity-modulated EM wave 824indicates that a desired level of neural activity is being produced bythe interference signal.

Although FIG. 8 depicts the same target region being stimulated andsensed, it is also possible for one or more first target regions to beneurally stimulated by the neuromodulator portion of the system andneural activity sensed from one or more second target regions. Thesystem may be configured to write in neural stimulation and read outneural activity from multiple target regions within the body. The systemmay be configured to write-in neural stimulation at one or more firstlocations and read out neural activity from one or more secondlocations. For example, consider a system capable of addressing multipletarget regions within the body. The system may simultaneously write inneural stimulation to each of the multiple target regions. The systemmay sequentially write in neural stimulation to each of the multipletarget regions or may sequentially write in neural stimulation to one ormore groups of the multiple target regions. Similarly, the system maysimultaneously read out neural activity from each of the multiple targetregions. The system may sequentially read out neural activity from eachof the multiple target regions or may sequentially read out neuralactivity from one or more groups of the multiple target regions. In someimplementations, the system may write in neural stimulation to one ormore first target regions and may read out neural activity from one ormore second target regions.

The foregoing description of various embodiments has been presented forthe purposes of illustration and description and not limitation. Theembodiments disclosed are not intended to be exhaustive or to limit thepossible implementations to the embodiments disclosed. Manymodifications and variations are possible in light of the aboveteaching.

1. A system, comprising: a neuromodulator comprising: an electromagnetic(EM) wave generator configured to generate EM waves remote from apatient and to direct the EM waves to one or more target regions withinthe patient, frequencies of the EM waves falling outside a range offrequencies that activates neurons, intersection of the EM waves in eachtarget region creating envelope-modulated electric and magnetic fieldshaving one or more frequencies that fall within the range of frequenciesthat activates neurons; and control circuitry configured to controlparameters of the EM waves produced by the EM wave generator.
 2. Thesystem of claim 1, wherein the frequencies of the EM waves are greaterthan about 150 kHz and frequencies of the envelope-modulated electricand magnetic fields are less than about 100 kHz.
 3. The system of claim1, wherein the control circuitry is configured to control one or moreparameters of the EM waves to change one or more characteristics of theenvelope-modulated electrical and magnetic fields in the target regions.4. The system of claim 3, wherein: the one or more parameters thatchange the characteristics of the envelope-modulated electrical andmagnetic fields include frequency, phase, and amplitude; and the one ormore characteristics of the envelope-modulated electrical and magneticfields include frequency, amplitude, and modulation depth.
 5. The systemof claim 1, wherein: the EM wave generator comprises a phased arrayconfigured to generate multiple EM waves; and the control circuitry isconfigured to control one or more parameters of the multiple EM wavessuch that the multiple EM waves undergo constructive and destructiveinterference that focuses and/or steers the multiple EM waves to thetarget regions.
 6. The system of claim 1, wherein an amplitude of theenvelope modulated electric field exceeds a threshold for neuralactivation.
 7. The system of claim 1, wherein an amplitude of theenvelope modulated electric field is below a threshold for activation ofneurons within the target region.
 8. The system of claim 1, wherein aminimum volume in which neurons are activated by the neuromodulationdevice without activating neurons outside the volume is less than about125 cm³.
 9. The system of claim 1, wherein a maximum amplitude of theenvelope modulated electric field falls within the target region. 10.The system of claim 1, further comprising communications circuitryconfigured to transfer patient information from an additional device tothe neuromodulation device; and wherein the control circuitry isconfigured to modify parameters of at least one of the first and secondEM waves based on the patient information.
 11. The system of claim 10,wherein the patient information comprises sensed physiological signals.12. The system of claim 10, wherein the patient information are based onpatient-provided input.
 13. The system of claim 1, further comprising areceiver configured to receive EM waves modulated by a neural activitysignal generated by neural activity within the target region.
 14. Thesystem of claim 13, wherein the control circuitry is configured to:extract the neural activity signal from the EM waves modulated by theneural activity signal; and control parameters of the EM waves based onthe neural activity signal.
 15. A method, comprising: generatingelectromagnetic (EM) waves at a location remote from a patient,frequencies of the EM waves falling outside a range of frequencies thatactivate neurons; directing the EM waves to one or more target regionwithin the patient; and intersecting the EM waves in the target regions,in each target region, intersection of the EM waves creatingenvelope-modulated electrical and magnetic fields having frequenciesfalling within the range of frequencies that activate neurons.
 16. Themethod of claim 15, further comprising controlling one or moreparameters of the first and second EM waves to change one or morecharacteristics of the envelope-modulated electrical and magnetic fieldsin the target regions.
 17. The method of claim 15, further comprisingreceiving EM waves modulated by a neural activity signal generated byneural activity within the target region.
 18. The method of claim 17,further comprising modifying parameters of the first and second EM wavesbased on the EM wave modulated by neural activity signal.
 19. The methodof claim 15, further comprising modifying parameters of the first andsecond EM waves based on patient information transferred from anadditional device.
 20. The method of claim 19, wherein the additionaldevice is a physiological sensor implanted within or attached to thepatient.
 21. The method of claim 19, wherein: the additional deviceincludes a user interface that allows the patient to input the patientinformation; and modifying the parameters comprises modifying theparameters based on information input by the patient.